content: /*
   * Copyright 2017 David Karnok
   *
   * Licensed under the Apache License, Version 2.0 (the "License");
   * you may not use this file except in compliance with the License.
   * You may obtain a copy of the License at
   *
   *     http://www.apache.org/licenses/LICENSE-2.0
   *
   * Unless required by applicable law or agreed to in writing, software
   * distributed under the License is distributed on an "AS IS" BASIS,
   * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
   * See the License for the specific language governing permissions and
   * limitations under the License.
   */
  
  package hu.akarnokd.reactive4javaflow.processors;
  
  import hu.akarnokd.reactive4javaflow.FolyamSubscriber;
  
  import java.util.*;
  import java.util.concurrent.Flow;
  
  final class SerializedFolyamProcessor<T> extends FolyamProcessor<T> implements Flow.Subscription {
  
      final FolyamProcessor<T> actual;
  
      Flow.Subscription upstream;
  
      boolean emitting;
      boolean missed;
      boolean done;
  
      List<T> queue;
      Throwable error;
  
      public SerializedFolyamProcessor(FolyamProcessor<T> actual) {
          this.actual = actual;
      }
  
      @Override
      public boolean hasThrowable() {
          return actual.hasThrowable();
      }
  
      @Override
      public Throwable getThrowable() {
          return actual.getThrowable();
      }
  
      @Override
      public boolean hasComplete() {
          return actual.hasComplete();
      }
  
      @Override
      public boolean hasSubscribers() {
          return actual.hasSubscribers();
      }
  
      @Override
      protected void subscribeActual(FolyamSubscriber<? super T> s) {
          actual.subscribe(s);
      }
  
      @Override
      public void onSubscribe(Flow.Subscription subscription) {
          upstream = subscription;
          actual.onSubscribe(this);
      }
  
      @Override
      public void onNext(T item) {
          Objects.requireNonNull(item, "item == null");
          synchronized (this) {
              if (emitting) {
                  if (!done) {
                      List<T> q = queue;
                      if (q == null) {
                          q = new ArrayList<>();
                          queue = q;
                      }
                      q.add(item);
                      missed = true;
                  }
                  return;
              }
              emitting = true;
          }
  
          actual.onNext(item);
  
          for (;;) {
              List<T> q;
              boolean d;
              Throwable ex;
              synchronized (this) {
                  if (!missed) {
                      missed = false;
                      emitting = false;
                      return;
                  }
                  missed = false;
                  q = queue;
                  queue = null;
                  d = done;
                  ex = error;
              }
  
              if (q != null) {
                  for (T v : q) {
                      actual.onNext(v);
                  }
              }
  
              if (d) {
                  if (ex == null) {
                      actual.onComplete();
                  } else {
                      actual.onError(ex);
                  }
                  return;
              }
          }
  
      }
  
      @Override
      public void onError(Throwable throwable) {
          Objects.requireNonNull(throwable, "throwable == null");
          synchronized (this) {
              if (emitting) {
                  if (!done && error == null) {
                      error = throwable;
                      done = true;
                      missed = true;
                  }
                  return;
              }
              emitting = true;
              done = true;
          }
  
          actual.onError(throwable);
      }
  
      @Override
      public void onComplete() {
          synchronized (this) {
              if (emitting) {
                  done = true;
                  missed = true;
                  return;
              }
              emitting = true;
              done = true;
          }
  
          actual.onComplete();
      }
  
      @Override
      public void request(long n) {
          upstream.request(n);
      }
  
      @Override
      public void cancel() {
          upstream.cancel();
      }
  }
  